Engine

ABSTRACT

An oil recovery part ( 20 A,  20 B) for guiding oil to an inner side of a peripheral wall of a cylinder head ( 2 ) is provided at a front wall upper end of the cylinder head ( 2 ), the oil leaking from a concave bearing (3 a,    3   b ) that supports a camshaft ( 8, 9 ) provided at a forefront end of a cam housing ( 3 ).

FIELD OF THE INVENTION

This invention relates to an engine (also called internal combustionengine) in which a camshaft is supported rotatably by a cam housingattached onto a cylinder head, and more particularly to an improvedstructure for oil to flow from a supporting part of a journal partpositioned at a forefront end of the camshaft.

BACKGROUND OF THE INVENTION

Japanese Patent Application Publication No. 5-86913 (JP-A-5-86913)discloses an engine mounted with a hydraulically-driven variable valvetiming mechanism for changing valve timing.

This variable valve timing mechanism is a mechanism capable of changingthe timing of opening and closing at least one of intake and exhaustvalves by advancing or retarding a rotational phase of at least one ofintake and exhaust camshafts in relation to a rotational phase of acrankshaft.

The abovementioned hydraulically-driven variable valve timing mechanismhas a controller that is constituted by a vane actuator installed on thefront end side of the camshafts, and an oil control valve for adjustingthe pressure of working oil supplied to an advance-side pressure chamberand a retard-side pressure chamber of the controller.

This engine might be provided with a supply passage for pumping up oilof an oil pan (oil storage) provided on a bottom part of the engine byusing an oil pump and then supplying the oil to two systems of acylinder block system and a cylinder head system. Note that the oil thatlubricates the inside of the cylinder block and the inside of thecylinder head is returned to the oil pan, and thus the oil circulates ina closed loop within the engine.

The oil that is supplied to the cylinder block system is also suppliedto a crank journal, oil jet, and the like. The oil that is supplied tothe cylinder head system, on the other hand, is supplied in the form ofworking oil to the oil control valve of the variable valve timingmechanism described above.

Note that the oil that is supplied to the cylinder head system issupplied to a journal part positioned at a forefront end of a camshaftand to the oil control valve and each pressure chamber of the controllerof the variable valve timing mechanism via oil passages provided withina forefront-end cam cap attached to a concave bearing of a cam housingthat supports the forefront-end journal part. Note that the oil thatreturns from each pressure chamber of the controller is discharged intothe cam housing through the oil passages.

As in the related art described above, in a case where part of the oilpassages for supplying and recovering the oil to and from the controllerand oil control valve of the variable valve timing mechanism is providedin the cam cap and camshaft attached to the forefront-end concavebearing of the cam housing, there is a possibility that the oil flowingthrough the oil passages leaks from a sliding contact surface where theforefront-end concave bearing of the cam housing and the cam cap comeinto sliding contact with the journal part positioned at the forefrontend of the camshaft, into a timing chain cover.

This sliding contact surface is a part where the concave bearing and camcap come into sliding contact with the camshaft, and thus needs a gap ofappropriate thickness therebetween. For this reason, the oil leakageoccurs easily.

Therefore, when the oil that leaks into the timing chain cover contactswith the timing chain, there is a risk of friction loss that is causedby rotation resistance of a timing chain. Especially when the oilleaking from the sliding contact surface into the timing chain in spiteof the system that lubricates the timing chain using the oil, excessiveamount of oil is supplied to the timing chain, resulting in unexpectedgrow of friction loss.

Since it is desired to alleviate the friction loss as much as possiblein view of improving engine efficiency and fuel consumption performance,there is room for improvement.

Note that even in an engine that is not mounted with the above variablevalve timing mechanism, oil leaks from a sliding contact surface where aforefront-end journal part of the camshaft comes into sliding contactwith the concave bearing of the cam housing and with the cam cap.

SUMMARY OF THE INVENTION

This invention provides an engine in which a camshaft is rotatablysupported by a cam housing mounted on a cylinder head, wherein oil thatleaks from a supporting part provided at a forefront end of the camshaftis caused not to contact with a timing chain so that unexpected grow offriction loss can be inhibited or prevented.

A first aspect of this invention relates to an engine in which acamshaft is rotatably supported by a cam housing mounted on a cylinderhead. This engine has: the cylinder head; a cam housing mounted on thecylinder head; a camshaft supported rotatably by the cam housing; aforefront-end concave bearing which is provided at a front wall upperend of the cylinder head and which supports the camshaft supported bythe cam housing; and an oil recovery part for guiding oil leaking fromthe concave bearing to an inner side of a peripheral wall of thecylinder head.

According to this constitution, even if the oil leaks from the concavebearing that supports the camshaft provided at a forefront end of thecam housing, this leaking oil can be guided from the oil recovery partto the inner side of the peripheral wall of the cylinder head.Therefore, the phenomenon in which excessive amount of oil is suppliedto the timing chain as in the related art can be avoided. Consequently,unexpected grow of friction loss that occurs in the related art can beinhibited or prevented.

The oil recovery part may have a projecting part that is provided in aregion corresponding to the concave bearing at the front wall upper endof the cylinder head, and a groove that is provided in the projectingpart and receives and guides the leaking oil to the inner side of theperipheral wall of the cylinder head.

Specifying the constitution of the oil recovery part in this mannermakes it easier to understand the pattern of recovering the leaking oil.

The oil recovery part may have, at a front end thereof, a rising wallthat extends upward.

This engine may further have a tapered slope that is provided at a frontend lower corner of the forefront-end concave bearing of the camhousing.

The inclination of the tapered slope may be formed such that a rear endthereof is positioned lower than a front end thereof.

According to this constitution, a front opening of the groove isenlarged by the presence of the slope, whereby the leaking oil can bereceived easily and recovery operation is improved.

The oil recovery part may be provided below the concave bearing suchthat the front end of the oil recovery part is positioned forward of theforefront end of the concave bearing and a rear end of the oil recoverypart is positioned on the inner side of the peripheral wall of thecylinder head.

A second aspect of this invention relates to an engine. This engine has:a cylinder head; a cam housing mounted on the cylinder head; an intakecamshaft and exhaust camshaft that are supported rotatably by the camhousing; a hydraulically-driven variable valve timing mechanism whichhas a controller constituted by a vane actuator installed at a front endof at least one of the intake camshaft and the exhaust camshaft, and anoil control valve for adjusting supply/recovery of working oil withrespect to the controller, and which is capable of changing a timing ofopening and closing at least one of an intake valve and an exhaust valveby advancing or retarding a rotational phase of at least one of theintake camshaft and exhaust camshaft in relation to a rotational phaseof a crankshaft; a forefront-end side journal part of the camshaft,which is provided with a part of an oil passage connecting thecontroller to the oil control valve; a concave bearing which is providedat a front wall upper end of the cylinder head and which supports thecamshaft provided at a forefront end of the cam housing; and an oilrecovery part that guides, to an inner side of a peripheral wall of thecylinder head, oil leaking from a sliding contact surface between theforefront-end side journal part of the camshaft and the concave bearing.

In this constitution provided with the variable valve timing mechanismas described above, oil hardly leaks from the concave bearing thatsupports the camshaft provided at the forefront end of the cam housing.

Specifically, when a part of the oil passage or supplying and recoveringthe oil to and from the controller and oil control valve of the variablevalve timing mechanism is provided in a cam cap or the camshaft attachedto the forefront-end concave bearing of the cam housing, there is a riskthat the oil flowing through the oil passage leaks from a slidingcontact surface where the concave bearing positioned at the forefrontend of the cam housing comes into sliding contact with the journal partposition at the forefront end of the camshaft, into a timing chaincover.

However, even when such oil leakage occurs, the above constitutionenables guiding of the leaking oil to the inner side of the peripheralwall of the cylinder head through the oil recovery part. Consequently,the phenomenon in which excessive amount of oil is supplied to thetiming chain as in the related art can be avoided. As a result,unexpected grow of friction loss that occurs in the related art can beinhibited or prevented.

The engine further has: a conveyance passage for supplying the oil,which is pumped up from an oil pan by an oil pump, to the oil controlvalve; and an advance-side oil passage and a retard-side oil passage forexchanging the oil between the oil control valve and advance-side andretard-side pressure chambers of the controller. The advance-side oilpassage and the retard-side oil passage may be each configured by atleast combining a first part that is provided over an area between theoil control valve and an outer peripheral surface of the forefront-endjournal part of the camshaft, and a second part that is connected fromthe first part to each of the pressure chambers through the inside ofthe camshaft.

According to this constitution, the oil flowing through the advance-sideoil passage and the retard-side oil passage might leak from the concavebearing that supports the camshaft provided at the forefront end of thecam housing. Specifically, the above description specifies one exampleof the constitution where oil leakage might occur. However, the oil thatmight leak is guided to the inner side of the peripheral wall of thecylinder head as described above, and is inhibited or prevented fromfalling onto an external side of the peripheral wall, that is, aninternal space of the timing chain cover.

According to this invention, even when the oil leaks from the supportingpart provided at the forefront end of the camshaft, this oil can becaused not to contact with the timing chain. Therefore, unexpected growof friction loss that occurs in the related art can be inhibited orprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is an arrow view of a cross section taken along the line I-I ofFIG. 6, wherein an engine according to a first embodiment of theinvention is shown;

FIG. 2 is a perspective view showing the front of a state in which a camcap of FIG. 1 is separated;

FIG. 3 is a perspective view showing a state in which a cylinder headand cam housing shown in FIG. 2 are separated;

FIG. 4 is an exploded perspective view of a part of the engine used ineach embodiment of the invention;

FIG. 5 is a side view showing a fractured front end side of the engineof FIG. 4;

FIG. 6 is a front view showing a state in which a timing chain cover isremoved from the engine shown in FIG. 5;

FIG. 7 is a view schematically showing hydraulic paths of intake andexhaust variable valve timing mechanisms mounted in the engine shown inFIG. 4;

FIG. 8 is a perspective view showing forefront ends of the cam cap ofthe engine shown in FIG. 4;

FIG. 9 is a view showing the front of the cam cap of FIG. 8;

FIG. 10 is a view showing an engine according to a second embodiment ofthe invention, the view corresponding to FIG. 1;

FIG. 11 is a view of the second embodiment corresponding to FIG. 2; and

FIG. 12 is a view of the second embodiment corresponding to FIG. 3.

DETAILED DESCRIPTION OF EMBODIMENTS

The best embodiments of the invention are described hereinafter indetail with reference to FIGS. 1 to 12. First, a first embodiment of theinvention is shown in FIGS. 1 to 9.

An overview of an engine used on the first embodiment is described withreference to FIGS. 4 to 6.

FIG. 4 is an exploded perspective view showing a part of the enginecommon to the embodiments of the invention. FIG. 5 is a side viewshowing a fractured front end side of the engine of FIG. 4. FIG. 6 is afront view showing a state in which a timing chain cover is removed fromthe engine shown in FIG. 5.

In the engine of this specification, the side in which a timing chain(or a timing belt) is disposed represents the front of the engine inorder to clarify the meanings of “front end” and “rear end.”

Note that the basic configuration or principle of operation of theengine is a conventional matter, the parts related to thecharacteristics of the first embodiment are described in detail, andthus the detailed description of the parts that are not related directlyto the characteristics of the first embodiment is omitted.

The engine shown in the drawings is, for example, a four-cylinder DOHCgasoline engine. In each drawing, reference numeral 1 represents acylinder block, 2 a cylinder head, 3 a cam housing, 4 a cam cap, 5 atiming chain (or a timing belt), 6 a timing chain cover (or a timingbelt cover), and 7 a cylinder head cover.

The cylinder head 2 is mounted with, although not shown, an intake valvefor opening and closing an intake port and an exhaust valve for openingand closing an exhaust port 2 a (only shown in FIG. 1). The cam housing3 is mounted with an intake camshaft 8 for opening and closing theintake valve and an exhaust camshaft 9 for opening and closing theexhaust valve.

A pair of the camshafts 8, 9 are mounted on a plurality of pairs ofconcave bearings 3 a, 3 b provided in a plurality of sections of the camhousing 3 in a front-back direction thereof, and the cam cap 4 isfastened by bolts 15A to the top of each pair of concave bearings 3 a, 3b arranged in a width direction of the engine, whereby axial and radialpositions of each of the camshafts 8, 9 are determined.

Note that the cam cap 4 is fastened to the cam housing 3 by two shortbolts 15A as shown in FIG. 2, and the cam cap 4 and the cam housing 3are fastened to the cylinder head 2 by three long bolts 15B.

The sections in the camshafts 8, 9 that are supported by the concavebearings 3 a, 3 b and the cam cap 4 are called “journal parts 8 a, 9 a,”respectively.

Note that the abovementioned intake valve, exhaust valve, intakecamshaft 8 and exhaust camshaft 9 are generically called “valvemechanism.” This valve mechanism is covered from the outside by thecylinder head cover 7 attached to an upper part of the cylinder head 3.Although depending on the type of the engine, this valve mechanism alsoincludes a lock arm and lash adjuster.

The intake camshaft 8 and the exhaust camshaft 9 are driven to rotate bya crankshaft 11 via the timing chain 5.

The timing chain 5 is wound around a timing gear 12 provided on one endof the intake camshaft 8 in an axial direction thereof, a timing gear 13provided on one end of the exhaust camshaft 9 in an axial directionthereof, and a timing gear 14 provided on one end of the crankshaft 11in an axial direction thereof.

The timing chain 5 and the three timing gears 12 to 14 configure a powertransmission system for transmitting torque from the crankshaft 11 toeach of the camshafts 8, 9. This power transmission system is generallydisposed on an external side of a front wall of the cylinder block 1,the cylinder head 2 and cam housing 3, and is covered and protected bythe timing chain cover 6 attached to the front wall of the cylinderblock 1, the cylinder head 2 and cam housing 3.

Here, the engine is designed such that oil contained in an oil pan 16can be repeated circulated and used within the engine.

Specifically, the oil that is contained in the oil pan 16 provided on abottom part of the cylinder block 1 is pumped up by an oil pump drivenby the crankshaft 11, filtered through a filter, and then supplied tothe cylinder block 1 side and the cylinder head 2 side.

The oil supplied to the cylinder block 1 side is returned to the oil pan16 after being used for lubricating a crankshaft journal part and theinside of a cylinder by means of an oil jet. The oil supplied to thecylinder head 2, on the other hand, is returned to the oil pan 16 afterbeing used for lubricating each of the components configuring the valvemechanism.

Incidentally, the engine described above is equipped with a variablevalve timing (VVT) mechanism.

This variable valve timing mechanism is capable of adjusting the valvetiming (opening and closing) of the intake valve and exhaust valve bycontinuously changing phases of the intake camshaft 8 and of the exhaustcamshaft 9.

This variable valve timing mechanism is of hydraulically-driven type.This variable valve timing mechanism is configured by VVT controllers30, 40 and a control system (including oil control valves 50, 60, anelectronic control device etc., not shown), as shown in FIG. 7.

The VVT controllers 30, 40, called “vane actuators” of conventionaltype, are configured mainly by outer rotors 31, 41 and vane rotors 32,42.

The VVT controllers 30, 40 are annexed, respectively, to front ends ofthe camshafts 8, 9 so as to be disposed on an external side of a frontwall of the cylinder block 1, and covered and protected by the timingchain cover 6 as shown in FIG. 5, as with the power transmission systemdescribed above.

The timing gears 12, 13 that are provided respectively on the ends ofthe intake camshaft 8 and exhaust camshaft 9 in the axial directionsthereof are integrally provided on outer diameters of the outer rotors31, 41, respectively. Specifically, the outer rotors 31, 41 are drivenby the crankshaft 11.

The vane rotors 32, 42 are attached, respectively, to the front ends ofthe intake camshaft 8 and exhaust camshaft 9 so as to be rotatable, andaccommodated, respectively, in the outer rotors 31, 41 so as to be ableto swing relative to each other in a circumferential direction.

Several sections on an inner periphery of each of the outer rotors 31,41 are provided with concave parts 31 a, 41 a that are recessed radiallyoutward, and several sections on an outer periphery of each of the vanerotors 32, 42 are provided with vanes 32 a, 42 a that protrude radiallyoutward (the same number as the number of concave parts 31 a, 41 a).

Each vane 32 a, 42 a of the vane rotor 32, 42 is inserted into thecorresponding concave part 31 a, 41 a of the outer rotor 31, 41 so as tobe able to swing in the circumferential direction, and an advance-sidepressure chamber 33, 43 and retard-side pressure chamber 34, 44 aresecured on each side of each vane 32 a, 42 a in the circumferentialdirection in each concave part 31 a, 41 a.

Note that the number of concave parts 31 a of the intake outer rotor 31and the number of vanes 32 a of the intake vane rotor 32 are both three,while the number of concave parts 41 a of the exhaust outer rotor 41 andthe number of vanes 42 a of the exhaust vane rotor 42 are both four asshown in FIG. 7. Therefore, three advance-side pressure chambers 33 andthree retard-side pressure chambers 34, i.e., a total of six pressurechambers, are provided in the intake controller 30, while fouradvance-side pressure chambers 43 and four retard-side pressure chambers44, i.e., a total of eight pressure chambers, are provided in theexhaust controller 40.

The oil control valves 50, 60 adjust the amount of working oil to besupplied to the advance-side pressure chambers 33, 43 or retard-sidepressure chambers 34, 44 and the amount of working oil to be returnedfrom the advance-side pressure chambers 33, 43 or retard-side pressurechambers 34, 44. Although the oil control valves 50, 60 are notillustrated in detail, the oil control valves 50, 60 are of conventionalelectromagnetically-driven spool type.

Specifically, electromagnetic solenoids 51, 61 of the respective oilcontrol valves 50, 60 are controlled by an electronic control device(ECU), which is not shown, to displace an axial direction of spoolvalves (not shown) and open/close five ports 52 to 56, 62 to 66.Accordingly, the amount of working oil to be supplied to each of thepressure chambers 33, 43, 34, 44 and the amount of working oil to bereturned to each of the pressure chambers 33, 43, 34, 44 are adjusted todrive the intake camshaft 13 or the exhaust camshaft 14 to the advanceside or retard side.

Basic operations of the variable valve timing mechanism are described.

When advancing a valve timing, the working oil is supplied from advanceports 53, 63 of the oil control valves 50, 60 to the advance-sidepressure chambers 33, 43, respectively, as shown by the solid arrows inFIG. 7. In so doing, the working oil within the retard-side pressurechambers 34, 44 is returned to the oil control valves 50, 60.

Conversely, when retarding the valve timing, the working oil is suppliedfrom retard ports 54, 64 of the oil control valves 50, 60 to theretard-side pressure chambers 34, 44, respectively, as shown by thedashed arrows in FIG. 7. In so doing, the working oil within theretard-side pressure chambers 33, 43 is returned to the oil controlvalves 50, 60.

The working oil that is returned to the oil control valves 50, 60 isnormally discharged from drain ports 55, 56, 65, 66 into an internalspace surrounded by the cam housing 3 and the cylinder head cover 7.

Incidentally, the working oil used in the variable valve timingmechanism is oil that is supplied from the abovementioned oil pan 16 tothe cylinder head 2 side. This passage for distributing the working oilis described simply hereinafter with reference to FIGS. 7 to 9.

The abovementioned distribution passage is configured by, as shown inFIG. 7, a conveyance passage 71 that connects the oil control valves 50,60 to an upper end of a supply passage (not shown) for guiding oilpumped up by an oil pump 17 from the oil pan 16 to the cylinder head 2side, advance-side oil passages 72, 74 that connect the oil controlvalves 50, 60 to the advance-side pressure chambers 33, 43 of the VVTcontrollers 30, 40, respectively, and retard-side oil passages 73, 75that connect the oil control valves 50, 60 to the retard-side pressurechambers 34, 44 of the VVT controllers 30, 40, respectively.

The conveyance passage 71 shown in FIG. 7 is provided in the cam cap 4as shown in FIGS. 8 and 9, and is configured by a combination of acylindrical upstream part 71 a disposed horizontally in the middle ofthe cam cap 4 in its longitudinal direction, a cylindrical intermediatepart 71 b disposed horizontally along the longitudinal direction of thecam cap 4, and cylindrical downstream parts 71 c, 71 d that are openedupward at both ends of the intermediate part 71 b.

Note that the intermediate part 71 b is in the form of a horizontallydisposed cylinder that is closed by mounting lids on its holes that arepenetrated from its both ends through the longitudinal direction of thecam cap 4.

The advance-side oil passages 72, 74 and the retard-side oil passages73, 75 shown in FIG. 7 is configured by, as shown in FIGS. 8 and 9, acombination of parts provided in the cam cap 4 (vertically cylindricalthrough-holes 72 a, 73 a, 74 a, 75 a), parts provided in the intakecamshaft 8 and exhaust camshaft 9 (outer peripheral grooves 72 b, 73 b,74 b, 75 b shown only in FIG. 1 and L-shaped holes 72 c, 73 c, 74 c, 75c), and parts provided in the vane rotors 32, 42 (holes not shown).

Note that the outer peripheral grooves 72 b, 73 b, 74 b, 75 b areprovided at the positions matching with lower end openings of thethrough-holes 72 a, 73 a, 74 a, 75 a of the cam cap 4, and radialdirection parts of the L-shaped holes 72 c, 73 c, 74 c, 75 c are openedcircumferentially at predetermined positions of the bottom of the outerperipheral grooves 72 b, 73 b, 74 b, 75 b.

Therefore, even when the camshafts 8, 9 is rotated, the through-holes 72a, 73 a, 74 a, 75 a of the non-rotated cam cap 4 are always communicatedcoupled respectively with the L-shaped holes 72 c, 73 c, 74 c, 75 c ofthe camshafts 8, 9. Each of the L-shaped holes 72 c, 73 c, 74 c, 75 ccan be obtained by, for example, perforating it with a drill in theaxial direction and radial direction.

The sections applied with the characteristics of this embodiment are nowdescribed in detail.

Specifically, this embodiment is constituted such that leakage of theoil into the internal space of the timing chain cover 6 is inhibited oravoided by guiding the oil to the inner side of the peripheral wall ofthe cylinder head 2, the oil leaking from the sliding contact surfacewhere each of the forefront-end journal parts 8 a, 9 a of thecorresponding camshaft 8, 9 comes into sliding contact with each of theforefront-end concave bearings 3 a, 3 b of the cam housing 3 and withthe cam cap 4.

More specifically, at the front wall upper end of the cylinder head 2,oil recovery parts 20A, 20B are provided in the regions corresponding tothe two forefront-end concave bearings 3 a, 3 b of the cam housing 3.

These oil recovery parts 20A, 20B are configured, respectively, byprojecting parts 21A, 21B provided at the front wall upper end of thecylinder head 2 and grooves 22A, 22B provided in the projecting parts21A, 21B.

The projecting parts 21A, 2113 are provided only on, for example, thefront wall upper end side of the cylinder head 2, and thus the entirefront wall of the cylinder head 2 does not project. Therefore, theprojecting parts 21A, 21B are beneficial in preventing the increase inthe weight of this front wall as much as possible.

Moreover, the grooves 22A, 22B are each provided in an area between thepart that is inside and not far from the projecting edge of each of theprojecting parts 21A, 21B and the inner surface side of the peripheralwall of the cylinder head 2. This means that a rising wall exists on thefront end side of each groove 22A, 22B and the rear end side of thegroove 22A, 22B (inner surface side of the peripheral wall) is openedinward of the cylinder head 2. For this reason, the oil leaking from thesliding contact surface can easily enter the grooves 22A, 22B and isprevented from falling outside the peripheral wall of the cylinder head2 once entering the grooves 22A, 22B.

The upward opening of each of the grooves 22A, 22B is covered by a lowersurface of each of the concave bearings 3 a, 3 b provided at theforefront end of the cam housing 3, but a front part of the upwardopening of each of the grooves 22A, 22B is opened outward.

As described above, the first embodiment is constituted such that whenthe oil leaks from the sliding contact surface where each of theforefront-end journal part 8 a, 9 a of the corresponding camshaft 8, 9comes into sliding contact with each of the forefront-end concavebearings 3 a, 3 b of the cam housing 3 and with the cam cap 4, thisleaking oil is caused to drop into each of the grooves 22A, 22B of thecorresponding oil recovery parts 20A, 20B and guided from the groove22A, 22B to the inner side of the peripheral wall of the cylinder head2.

Therefore, because the oil can be drawn to the inner side of theperipheral wall of the cylinder head 2 even when it leaks from thesliding contact surface, leakage of the oil into the internal space ofthe timing chain cover 6 that occurs in the related art can be inhibitedor avoided. Therefore, the phenomenon in which excessive amount of oilis supplied to the timing chain 5 as in the related art can be inhibitedor prevented as well as unexpected grow of friction loss that occurs in,for example, the related art.

Note that this invention is not limited to the above embodiment, andthus all types of modifications or applications are possible within thescope of the claims and the scope equivalent to this scope. Followingsare the examples of such modifications or applications.

(1) The engine according to this invention is not limited to in-lineengines or V-type engines, and the number of cylinders is also notparticularly limited. Therefore, the engine of this invention may be agasoline engine or a diesel engine.

(2) The embodiment above has described an example in which the variablevalve timing mechanism is annexed to each of the intake camshaft 8 andthe exhaust camshaft 9, but this invention can be applied to an enginein which the variable valve timing mechanism is mounted in either theintake camshaft 8 or the exhaust camshaft 9. Moreover, the oil recoverystructure of this invention can be applied to an engine that is notprovided with the variable valve timing mechanism.

(3) A second embodiment of this invention is described in detail withreference to FIGS. 10 to 12.

The second embodiment also has oil recovery parts 20A, 20B thatbasically play the same roles as the oil recovery parts 20A, 20B of thefirst embodiment, but the structures of the oil recovery parts 20A, 20Bof the second embodiment are different from those of the firstembodiment.

Each of the oil recovery parts 20A, 20B is configured by a projectingparts 21A, 21B provided at a front wall upper end of a cylinder head 2,a groove 22A, 22B provided in the projecting part 21A, 21B, and atapered slope 23A, 23B provided at a front end lower corner of a concavebearing 3 a, 3 b provided at a forefront end of a cam housing 3.

Each of the grooves 22A, 22B is provided over the area between a leadingend of each of the projecting parts 21A, 21B and a front wall of thecylinder head 2, that is, along the entire length of the front wall ofthe cylinder head 2 in its front-back direction.

However, in this embodiment, only a front-half region of an upwardopening of the groove 22A, 22B is formed into a descending taperedslope; while a rear-half region is formed into a flat surface. In thismanner, when oil enters the groove 22A, 22B the oil can be caused toflow easily toward the inner side of the peripheral wall of the cylinderhead 2 but not to flow out of the peripheral wall of the cylinder head2. Note that each of the grooves 22A, 22 b may be entirely inclineddownward from a leading end of the peripheral wall of the cylinder head2 toward the inside of the cylinder head 2.

Also, by providing the abovementioned slopes 23A, 23B in the cam housing3, a lower end of an external surface of a front wall of the cam housing3 can be recessed deeper than an upper end of the external surface ofthe front wall of the cylinder head 2.

In this case, the upward opening of each of the grooves 22A, 22B iscovered by a lower surface of each of the concave bearings 3 a, 3 bprovided at the forefront end of the cam housing 3, but the front endside of the upward opening of the groove 22A, 22B is opened wide outwardof the peripheral wall of the cylinder head 2 due to the presence ofeach of the slopes 23A, 23B.

Therefore, by providing a large gap between each of the slopes 23A, 23Band each of the grooves 22A, 22B, the oil leaking from the forefront-endconcave bearing 3 a of the cam housing 3 can be received easily.

In this embodiment as well, operations and effects that are basicallythe same as those of the first embodiment can be obtained. Specifically,the oil, which leaks from the sliding contact surface where each of theforefront-end journal parts 8 a, 9 a of the corresponding camshaft 8, 9comes into sliding contact with each of the forefront-end concavebearings 3 a, 3 b of the cam housing 3 and with the cam cap 4, is drawnfrom each of the oil recovery parts 20A, 20B toward the inner side ofthe peripheral wall of the cylinder head 2. Consequently, the phenomenonin which excessive amount of oil is supplied to the timing chain 5 as inthe related art can be inhibited or prevented as well as unexpected growof friction loss that occurs in the related art.

The second embodiment in which the slopes 23A, 23B are provided below atleast the forefront-end concave bearings 3 a, 3 b at the externalsurface of the front wall of the cam housing 3 is more beneficial thanthe above-described embodiment, in view of achieving weight reduction.

While the invention has been described with reference to the exampleembodiments thereof, it is to be understood that the invention is notlimited to the described embodiments or constructions. On the otherhand, the invention is intended to cover various modifications andequivalent arrangements. In addition, while the various elements of thedisclosed invention are shown in various example combinations andconfigurations, other combinations and configurations, including more,less or only a single element, are also within the scope of the appendedclaims.

1. An engine, comprising: a cylinder head; a cam housing mounted on thecylinder head; a camshaft supported rotatably by the cam housing; aforefront-end concave bearing which is provided at a front wall upperend of the cylinder head and which supports the camshaft supported bythe cam housing; and an oil recovery part for guiding oil leaking fromthe concave bearing to an inner side of a peripheral wall of thecylinder head.
 2. The engine according to claim 1, wherein the oilrecovery part includes: a projecting part that is provided in a regioncorresponding to the concave bearing at the front wall upper end of thecylinder head; and a groove that is provided in the projecting part andreceives and guides the leaking oil to the inner side of the peripheralwall of the cylinder head.
 3. The engine according to claim 2, whereinthe oil recovery part has, at a front end thereof, a rising wall thatextends upward.
 4. The engine according to claim 2, further comprising atapered slope that is provided at a front end lower corner of theforefront-end concave bearing of the cam housing.
 5. The engineaccording to claim 4, wherein an inclination of the tapered slope isformed such that a rear end thereof is positioned lower than a front endthereof.
 6. The engine according to claim 1, wherein the oil recoverypart is provided below the concave bearing such that the front end ofthe oil recovery part is positioned forward of the forefront end of theconcave bearing and a rear end of the oil recovery part is positioned onthe inner side of the peripheral wall of the cylinder head.
 7. Anengine, comprising: a cylinder head; a cam housing mounted on thecylinder head; an intake camshaft and exhaust camshaft that aresupported rotatably by the cam housing; a hydraulically-driven variablevalve timing mechanism which has a controller constituted by a vaneactuator installed at a front end of at least one of the intake camshaftand the exhaust camshaft, and an oil control valve for adjustingsupply/recovery of working oil with respect to the controller, and whichis capable of changing a timing of opening and closing at least one ofan intake valve and an exhaust valve by advancing or retarding arotational phase of at least one of the intake camshaft and exhaustcamshaft in relation to a rotational phase of a crankshaft; aforefront-end side journal part of the camshaft, which is provided witha part of an oil passage connecting the controller to the oil controlvalve; a concave bearing which is provided at a front wall upper end ofthe cylinder head and which supports the camshaft provided at aforefront end of the cam housing; and an oil recovery part that guides,to an inner side of a peripheral wall of the cylinder head, oil leakingfrom a sliding contact surface between the forefront-end side journalpart of the camshaft and the concave bearing.
 8. The engine according toclaim 7, further comprising: a conveyance passage for supplying the oil,which is pumped up from an oil pan by an oil pump, to the oil controlvalve; and an advance-side oil passage and a retard-side oil passage forexchanging the oil between the oil control valve and advance-side andretard-side pressure chambers of the controller, wherein theadvance-side oil passage and the retard-side oil passage are eachconfigured by at least combining a first part that is provided over anarea between the oil control valve and an outer peripheral surface ofthe forefront-end journal part of the camshaft, and a second part thatis connected from the first part to each of the pressure chambersthrough the inside of the camshaft.